The invention relates to a device for controlling the beam alignment in satellite laser communications systems.
In connection with optical beam alignment systems for communications or interferoimetric applications in satellites there is often the requirement for aligning a laser beam with high precision between a base station and a counter station. The accuracy required for this is a function of the distance between the two stations and the divergence of the laser beam. In satellite networks both parameters are mostly firmly prescribed by the constellation of the satellites and the maximum output available to the laser. Therefore the required accuracy of alignment is only possible by means of appropriately sensitive sensors/actuators in combination with an elaborate control concept.
This is made additionally more difficult by the extreme limiting conditions of space applications, which often result in accelerated wear of the components. However, in order to obtain the desired accuracy throughout the entire service life in spite of this, a concept for an adaptive control on the basis of a digital signal processing system is proposed in what follows. The control systems for beam alignment used up to now were not optimal because of the special limiting conditions which apply in connection with their use in satellites. Analog regulating systems are only suitable in a limited way because of their poor flexibility and the problems with the compensation of time-variant processes connected with this. Since more complex structures (for example higher order status controllers, predictors) can only be realized at great expense, and the achieved accuracy is limited, they are hardly usable for employment in highly accurate beam alignment systems.
Although digital regulating systems on the basis of microcomputers offer a high degree of accuracy and permit the realization of more complex structures, they are rather unsuitable for rapid dynamic processes because of their long calculating times. As a rule, the execution of mathematical operations (*,/exp. sin) typical for performing beam alignment in particular requires a lot of time, since most processes do not directly support floating point operations. These must mostly be taken over by the software, because of which often indefensibly long idle times result in a technical regulating system.
It is therefore the object of the invention to create a device for controlling the beam alignment in satellite laser communications systems, by means of which the disadvantages of the prior art are avoided.
A device for the control of the beam alignment in satellite laser communications systems has a digital signal processor, which has been inserted between an input interface and an output interface, and to which a program memory and a data memory are separately connected, in which parameters are also stored, and which comprises sensors and actuators for aligning the laser beam with the counter station. The signal processor contains an intermediate memory for floating point and fixed point operations and further calculating units, as well as two access generators. Highly flexible and very efficient control systems can be implemented by the employment of such a digital signal processor. By means of an adaptive control it is still possible to operate beam alignment systems at full performance levels, even after components have been degraded. The adjustment outlay for the optical components is drastically reduced because of autocalibration.